Simple, Safe Optochemical Sensor Relies on Light

Photonics.comMay 2012
GIESSEN, Germany, May 23, 2012 — Using only the interaction between nanostructures and light, an optochemical sensor has been developed that is simpler, safer and more reliable than standard electrical sensors.

Researchers working on the European Union-funded Dotsense project have created an optical transducer using an array of a billion gallium nitride (GaN) and indium gallium nitride (InGaN) quantum dots within nanowires. They placed the wires in the liquid/gaseous environment to be monitored and shone an excitation light on it, inducing the photoluminescence properties of the nanostructures to change. The photoluminescent properties of the quantum dots change depending on the specific chemicals in the environment, leading to variations in the transducer’s light intensity, which can be read using common photodetectors.

Schematic setup of Dotsense integrated optical chemical sensor system. Chemically induced changes in the photoluminescence characteristics of the nano-optical transducer element (InGaN/GaN QD superlattice or InGaN/GaN NW heterostructure) are detected.
The system, which relies solely on light, is much easier to implement and much more sensitive than the standard practice of running current through nanostructures and measuring the resistance. The goal of the Dotsense project was merely to create a chemical sensor that did not rely on electrical contacts; the greatly increased sensitivity that came with it was a bonus.

"We take advantage of the chemical sensitivity and the high surface-to-volume ratio of the nanostructures without having to implement a more complicated processing technology. There's a lot less technological effort involved to deploy and use this kind of sensing system," said Martin Eickhoff, the Dotsense project coordinator at Justus Liebig University.

Furthermore, the new system is safer than the current one. Running electrical current through certain chemicals can be deadly, especially when there are pressurized or flammable chemicals. For this reason, they are a good match for sensor technology on aircrafts.

"On an aircraft, they could be used to monitor water quality, hydraulic fluid, gas leaks or fuel," Eickhoff said. "When we started the project, aeronautical applications were our main focus, but we soon realized that there are additional applications for this technology in many other industries."

The researchers believe that the new technology is very commercially viable because of its safety and reliability. Applications are also in home smoke alarms, health care and food processing. However, the technology is not ready for mass production just yet. Eickhoff said that much more research is needed. Part of the research team has created a spinoff project called Sinomics, which will continue development.

"I'm optimistic that over the coming years this technology will find several applications, and it will become cheaper and, hence, more commercially viable to start producing all-optical sensors," Eickhoff said.

The project received funding from the European Union's Seventh Framework Programme.

Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.